Process for manufacture of precipitated calcium carbonate



Sept. 6, 1927;

B. G. WOOD PROCESS FOR MANUFACTURE OF PRECIPITATED CALCIUM GARBONATEFiled Sept. 8 1925 Raf/IR) ZINE K/uv. [/ME y 1 [ma ma WHER- FZLTER k E QEmu ER fiK/ER Sam/585R Cal/0602 WATER t... i 3. a. i

- BTON G. WOOD, or Los AHGELES, CALEOBNIA, ABSIGNGR ro IVAN? LmE AND215;. B1 WACTUBE 9F PRECI'EATED GALGI'UH l1? .iji. COMPANY, DE LOSANGELES, CALHGBNIA, A CORPORATION 0F CALI- hpplloation filed September8, 1935. Serial No. eases.

This invention has to do with the manuiaoture of what is commonly knownas amorphous calcium carbonate; that is calcium carbonate in a li htfiocculent form. Although there may be some dilierence of-opinion as toany iorm of calcium carbonate being truly amorphous, rather thancrystalline, the term amorphous has been commonly applied to calciumcarbonate that is finely divided, is light in weight and has a physicalcharacteristic of softness rather than the caaracteristic hardnessusually associated with crystalline substances. Finely divided amorphouscarbonate has many valuable uses well known in the art. and unnecessaryhere to detail; in fact the commercial value of a carbonate ismeasurcdvery largely by its qualities of lightness and'softness and finedivisibility.

it is a general object of this invention to provide apparatub andprocess for the continuous economical manufacture of this desirable formof calcium carbonate.

' Processes have heretofore been used and have produced a carbonate ofhigh quality;

but so far as I am aware no continuous process has heretofore been usedcapable of producin a uniform product of high quality. Such being thegeneral object of my invention, there are various other and morespecifie objects, all of which will become more clearly apparent fromthe following detailed spccihcation wherein I describe preferred andillustrative forms of apparatus and process-that are typical embodimentsofiny invention; and for that purpose 1 refer to the accompanyindrawings, in which:

Fig. 1 is a iagram in the nature of a flow sheet illustrative of theapparatus and process; and

Fig. 2 is a diagrammatic vertical section of the carbonizing tower ofthe apparatus.

In practicing my proces I start with natural calcium carbonate, whichmay be more or less pure, depending upon the character of depositavailable. Although some calcium carbonate deposits are of high purity,it is not necessary in my process t at the original substances be freero m impurities, as the process itself tends to eliminate alargervariety of impurities that may occur in nature. The quarried or minedcarbonate is first in troduced to a continuous lime kiln 10, which mayconveniently be a kiln of the rotary type heated by somesuitablefurnace, all in man-1 ners well known to the art. By operating atsuitable temperature, the calcium carbonate is within this kilndecomposed to lime (calcium oxide) and carbon dioxide gas. The calciumoxide continuously discharged from the rotor lime kiln is taken to acontinuous lime slac or 11 wherein it is continuously .mixed with asuitable roportion of water to The Y This suspension is next takendirectly by pump 12 and pumped to the top of carbonizing tower 13. Inthis carbonizin tower the hydroxide suspension, introduce to the top ofthe tower through ipe 14; (see Fig. 2)-drops down into a note ed edgedtrough 30 that, by overflow at the edges, distributes the liquid evenlyover the uppermost one of apluralit of staggeredperforated shelves 15.The 'quid passes through the perforations and is showered down onto thenext shelf, to be thereupon showered onto the next, and so on to thebottom of the tower. At the same time that the liquid is being showereddown through the tower from shelf to shelf, the carbon-dioxide gas isbeing passed upwardly through pipe lfi. The gas necessarily follows asinuous'course around the shelves from the bottom to the top of thetower; the shelves being placed in staggered relation and a sptce 15being left at the end of each shelf 12 :ge enough to pass the flow ofcarbon dioxide gas; Thus in the space between any two shelves, the gasis flowing more or less horizontally and the li uid is being showereddown vertically throug that horizontal flow of gas. Any excess gas (anyexcess carbon dioxide and all other gases, such as nitrogen) may pass 0Ethrough pipe 17 at the top of the tower either to storage or toatmosphere. The liquid accumulating in the bottom of. the tower, beingwater upon the amount of carbonate the amount of water being driven offwhich carrying the now 'formedcalcium carbonate in sus ension, passesoff through pipe 18 and goes irectly to a continuous filter 20 which maybe of any suitable type,for instance a rotary vacuum filter of knowntype may be used. From this filter the separated calcium carbonate,still wet but freed of all excess water, goes directly to drier 21 fromwhich the dry finely divided. calcium carbonate in the amorphous form isdelivered for packrier 21 may be-ot any suitable form; there are severalknown driers which 0B- eratecontinuously to dry finely divided sustances either in direct contact with a heated gas or by passing overplates heated by such gas. Whatever the specific form of the drier mabe, the drier obtains its heat from the car on dioxide gas comingdirectly from lime kiln 10. This carbon dioxide gas leaves the lime kilnat a temperature of 1000 F, to 1300 F., and innormal operatin conditionsit may leave the drier at a su stantially lower temperature; thelowering of temperature depending; of course, eing dried,

in turn depends upon the efiiciency of filter 20) and also upon the heattransfer efficiency of the drier itself.- Itis always the case, however,that calcium carbonate passing through the drier is freed of allmoisture so that it is delivered entirely dry; and the temperature towhich the carbon dioxide gas has fallen in the drier is of no particularconse uence as it is necessary, as I now point out, t at the carbondioxide gas be relatively cool when it is introduced to the carbonizingtower.

Ordinarily the heat transfer in drier 21 is not sufficient to cool thecarbon dioxide to the temperature desired, and accordingly the carbondioxide is led from the drier to a scrubber 22 through which water issprayed not only to clean the gas, but also to cool it to the pro erworking'temperature, which I find to e about 95 F. The water from thescrubber may be taken to a cooling tower so that it may be reused in theprocess, it being desirable to introduce cold or cool water to the limeslacker in order to prevent generation of too hi h temperatures there.The water for t e scrubber goes directly from filter 20; and thetemperature of the gas as it is taken from the scrubber may be regulatedby regulating the amount of water scrubber.

From the scrubber the cooled carbon dioxide gas is taken b a blower 23and blown into the bottom 0 carbonizing I tower 13, whereit passes upthrou h the down showering hydroxide as be ore described. As the gaspasses upwardly through the tower and the hydroxide showers down throughsprayed through the it, the hydroxide comes into very intimate contactwith the carbon dioxide, it being constantly in an atmosphere of thatgas, and being by reason of its suspension in water, in very finelydivided form. Each minute particle of hydroxide is by reaction with thegas converted to a minute particle of carbonate; and due to thecomparatively low temperature kept in the tower by reason of lowtemperature of gas, all these minute particles are prevented fromcoalescing to form large and hard crystalline masses. I have found thatif the operations in the tower'are carried on at a temperature muchhigher than ap roximately 95 F., there is a marked ten ency for thecarbonate to gather in large hard aggregate masses, thus preventing theattainment of that amorphous quality which it is the object of thisprocess to produce. By thus keeping the temperature comparatively low,the formed carbonate is carried down in the showering water in finelydivided form and in suspension, and goes to the filter in finesuspension. Neither in the filter nor in the drier, is there anytendency for the carbonate, formed in the manner described, to cake orform aggregate masses, so that the final product deand is what is knownas soft amorphous quality.

By introducing the carbon-dioxide gas to the tower at about 95 F., Ifind that I maintain the operating temperature in the tower at about thesame point or at about I livered from the drier is very finely divided,

pheric temperature may make it necessary to vary the temperature atwhich the gas is delivered to the tower from time to time in order tomaintain the proper reaction temperature. However, under averageatmospheric conditions, and where the water that goes into the limeslacker is cooled to substantially atmospheric temperature, thetemperature of the water hydroxide suspension going to the tower willnot ordinarily be much, if any, above 95 F. Should conditions be suchthat the temperature of the suspension coming to the tower should bematerially higher, then it may become desirable to cool the carbondioxide gas to a lower temperature so as to maintain the correctreaction temperatures in the tower.

I claim:

1. The herein described process for making amorphous calcium carbonate,that includes decomposing calcium carbonate to form lime and carbondioxide, slacking'the formed lime, passing the resultant calciumhydroxide into intimate contact with the carbon dioxide gas cooled toapproximately d perature of the carbon dioxide 5 Leagues 95 F., to formcalcium carbonate, iree' the formed calcium carbonate of water, an ryingthecarbonate and reducing the temas before ringing it into contact withthe ydroxide by drying the formed calcium carbonate by direct contactwith the heated carbon dioxide gas resulting from the decomposition, 2.The herein described process of roduc- 10 ing amorphous calciumcarbonate, t at includes decomposing calcium carbonate .to form lime andcarbon dioxide gas, slacking the lime with an excess of cool water toform a suspension of calcium hydroxide in 1 water at a tem erature ofabout 95 F,

showering said ydroxide suspension down through a suitable towerupwardly through whichthe carbon dioxide gas is passed to come intointimate contact with the calcium 20 hydroxide to form calcium carbonatein suspension in the water, segirating the suspended calcium carbonateom calcium carbonate b direct contact with the carbon dioxide pro ucedby the original decomposition, and thereb partially cooling thecarbon-dioxide; furt er coolin the'carbon dioxide to ap roximately 95 byinterchange of heat etween it and water from the filtering operation,and then passing the cooled carbon dioxide gas upwardly through thetower as aforesaid.

3. The process of making amorphous calcium carbonate, that inc udespassing a water suspension. of calcium hydroxide mto intimate and finelydivided contact with carbon dioxide gas at a temperature of about 95 F.,with the resulting formation of finely divided calcium carbonate andthen freeing the calcium carboiiate from the accompanying water.

In witness that have hereunto subscribed my name t is 9th day of July,1925.

BURTON G. WOOD.

I claim the fore ing I

